1. Field of the Invention
The various embodiments described herein relate to an optical touch panel, and, more particularly, to a multi-point optical touch panel.
2. Background of the Related Art
A variety of touch panel technologies are presently in existence, including resistive technology, capacitive technology, surface acoustical wave (SAW) technology, infrared (IR) technology, etc. Comparing with other touch panel technologies, IR technology has lots of advantages, for example, better durability, reliability, sealability, and no calibration required etc.
In the case of IR touch panel technology, infrared emitter/collector pairs are used to project an invisible grid of light a small distance over the surface of the panel. When a beam is interrupted, the absence of the signal at the collector is detected and converted to touch coordinates (e.g., X/Y rectangular coordinates). Since the method of determining a touch is optical instead of electrical or mechanical, IR touch panels are not as sensitive to damage as some technologies, such as resistive and capacitive technologies.
The construction of a conventional optical touch panel is disclosed in U.S. Pat. No. 6,597,508, which is incorporated herein by reference. FIG. 1 shown in the US patent depicts the construction of a conventional optical touch panel. The optical touch panel comprises a plurality of light-emitting elements (e.g., LEDs) arranged along two adjacent sides of a rectangular position-detecting surface and a plurality of light-receiving elements (e.g., photo transistors) 130 arranged along the other two sides of the rectangular position-detecting surface such that the light-emitting elements 110 are positioned opposite to the respective light-receiving elements and the position-detecting surface is positioned between the light-emitting elements and the light-receiving elements. In the optical touch panel, however, the light-emitting elements and the light-receiving elements must be arranged along the four sides of the position-detecting surface, and hence it takes a significant amount of time to establish wire connections among the elements. Thus, the optical touch panel is complicated, its assembly difficult, and it is difficult to reduce its size.
Another construction of a conventional optical touch panel is disclosed in Taiwan Patent Application No. 96151662, which is incorporated herein by reference.
With reference to FIG. 1A, a schematic diagram of the construction of an optical touch panel 101 shown in the Taiwan patent application No. 96151662 is provided. The optical touch panel 101 may comprise a rectangular position-detecting surface 150 with a specified length L and a specified width W (wherein L may be greater than or equal to W), a plurality of light-emitting element pairs (110a, 110b), two reflectors (e.g., mirrors) 120, and a plurality of light-receiving element pairs (130a, 130b). Each light-receiving element may be configured for receiving light beams reflected by the reflectors 120 or light beams directly emitted by the plurality of light-emitting element pairs without reflection. The plurality of light-emitting element pairs (110a, 110b) may comprise light emitting diodes (LEDs). The plurality of light-receiving element pairs (130a, 130b) may comprise photo transistors.
The plurality of light-emitting element pairs (110a, 110b) may be arranged at various points along a first side 110 of the rectangular position-detecting surface 150 in a lengthwise (L) direction. More specifically, there may be various points (e.g., point 0, point 1 . . . point L) along the first side 110 at which the plurality of light-emitting element pairs (110a, 110b) may be arranged. At each of these various points, other than the starting and the ending points (i.e., point 0 and point L, which are at the edges of the first side 110), a first light-emitting element (110a) and a second light-emitting element (110b) may be arranged in a pair [note that at the starting point (i.e., point 0), a second light-emitting element (110b) may be arranged, while at the ending point (i.e., point L), a first light-emitting element (110a) may be arranged]. The first light-emitting element (110a) may be arranged at the left side of each light-emitting element pair (110a, 110b) at an angle 180—θ with reference to the first side 110, and the second light-emitting element (110b) may be arranged at the right side of each light-emitting element pair (110a, 110b) at an angle θ with reference to the first side 110. The angle θ with reference to the first side 110 may be greater than an angle β, which may be the angle of the diagonal line of the rectangular position-detecting surface 150 with reference to the x-axis of the rectangular position-detecting surface 150. According to the exemplary embodiment of the Taiwan patent application No. 96151662, the angle θ may be 45 degrees, in which case the angle between the first light-emitting element (110a) and the second light-emitting element (110b) of each light-emitting element pair (110a, 110b) is 90 degrees.
Similarly, the plurality of light-receiving element pairs (130a, 130b) may be arranged at various points along a second side 130 opposite to the first side 110 of the rectangular position-detecting surface 150 in the lengthwise (L) direction. More specifically, there may be various points (e.g., point 0, point 1 . . . point L) along the second side 130 at which the plurality of light-receiving element pairs (130a, 130b) may be arranged. At each of these various points, other than the starting and the ending points (i.e., point 0 and point L, which are at the edges of the second side 130), a first light-receiving element (130a) and a second light-receiving element (130b) may be arranged in pair [note that at the starting point (i.e., point 0), a second light-receiving element (130b) may be arranged, while at the ending point (i.e., point L), a first light-receiving element (130a) may be arranged]. The first light-receiving element (130a) may be arranged at the left side of each light-receiving element pair (130a, 130b) at an angle θ—180 with reference to second side 130, and the second light-receiving element (130b) may be arranged at the right side of each light-receiving element pair (130a, 130b) at an angle −θ with reference to the second side 130. The angle θ with reference to the second side 130 may be greater than the angle β. According to an exemplary embodiment, the angle θ may be 45 degrees, in which case the angle between the first light-receiving element (130a) and the second light-receiving element (130b) of each light-receiving element pair (130a, 130b) is 90 degrees.
The two reflectors 120 may be arranged along two opposing sides of the rectangular position-detecting surface 150 in a widthwise (W) direction for reflecting light beams emitted by the plurality of light-emitting element pairs (110a, 110b).
In accordance with the exemplary embodiment as shown in FIG. 1A, given L=23 and W=19, each of the second light-receiving elements (130b) at points 0 through 4 may receive light beams emitted from the first light-emitting elements (110a) at points 19 through 23 respectively. Moreover, each of the first light-receiving elements (130a) at points 19 through 23 may receive light beams emitted from the second light-emitting elements (110b) at points 0 through 4 respectively. It is important to note that such transmissions of light beams are not explicitly illustrated in FIG. 1A but nevertheless are possible with respect to the optical touch panel 101 as depicted in FIG. 1A.
A control circuit (not shown) may be configured for causing the light-emitting element pairs (110a, 110b) to emit light beams in a predetermined order for the purpose of scanning the position-detecting surface 150. For instance, the light-emitting element pairs (110a, 110b) may emit light beams one-by-one in a sequential order from left to right, or a plurality of alternate light-emitting element pairs may simultaneously emit light beams at a given time. Moreover, the control circuit may be configured for causing the plurality of light-receiving element pairs (130a, 130b) to receive the light beams emitted from the plurality of light-emitting element pairs (110a, 110b). Accordingly, optical paths may be formed on the position-detecting surface 150 in a grid pattern as shown in FIG. 1A.
When an object (e.g., a pointing device such as a touch pin or a finger) is positioned at point M0 on the position-detecting surface 150 as shown in FIG. 1A, the object blocks a light beam 140 emitted by one of the first light-emitting elements (110a) and reflected by one of the reflectors 120. Moreover, the object at point M0 blocks a light beam 142 directly emitted by another of the first light-emitting elements (110a).
Due to the blockage of the light beam 140 and the light beam 142, two of the light-receiving elements do not receive these light beams. The two light-receiving elements that do not receive the light beams may be located at two points that respectively may be a distance ‘m’ and ‘n’ away from the left edge (i.e., point 0) of the second side 130 of the rectangular position-detecting surface 150. Accordingly, one of the two light-receiving elements not receiving a light beam may be “at a left portion” of the second side 130 and accordingly may be positioned at the point that is ‘m’ away from the left edge, while the other of the two light-receiving elements not receiving a light beam may be “at a right portion” of the second side 130 and accordingly may be positioned at the point that is ‘n’ away from the left edge. Similarly, the two light-emitting elements that correspond to the two light-receiving elements may be located at two points that respectively may be a distance ‘x’ and ‘y’ away from the left edge (i.e., point 0) of the first side 110 of the rectangular position-detecting surface 150.
Accordingly, the control circuit may be configured to determine the X/Y rectangular coordinates (A, B) of the object based on which light-receiving elements fail to receive a light beam during a scan cycle due to blockage of the light beam 140 and the light beam 142 at point M0.
If the object at point M0 blocks more than two light beams, the coordinates of the intended center position of the object may be determined by averaging the detected coordinate information. Such averaging may be completed by the control circuit or by another device operatively coupled to the optical touch panel 101.
In accordance with the exemplary embodiment of the Taiwan patent application No. 96151662, in order to determine the X/Y rectangular coordinates of the object positioned at point M0 on the position-detecting surface 150 in the event that the object blocks two light beams, the control circuit may be configured for dividing the position-detecting surface 150 into four regions I, II, III, and IV. These four regions I, II, III, and IV may be based on whether each of the two light-receiving elements not receiving a light beam is a first light-receiving element 130a or a second light-receiving element 130b of one of the plurality of light-receiving element pairs (130a, 130b). Since the length and the width ‘W’ of the position-detecting surface 150 and the positions of two of the light-receiving elements that do not receive the light beams may be given, equations to determine the X/Y rectangular coordinates (A, B) of point M0 respectively for the four regions I, II, III, and IV via geometric analysis can be obtained.
The problem for the optical touch panel 101, mentioned above, is that it will only be effective when a single point is detected. For example, when a user simultaneously touches two points, M2 and M4, on the position-detecting surface 150, the control circuit cannot determine the actual X/Y rectangular coordinates of points M2 and M4. The points M2 and M4 block four light beams, respectively as light beams 140, 142, 144 and 146. In such case, there will be six potential points (i.e. M0, M1, M2, M3, M4, M5) being obtained via the computation of the equations mentioned above based on the blocked light beams 140, 142, 144 and 146. Therefore, there exists other potential combinations of two points that block the same four light beams, e.g. points (M1 and M5) or (M0 and M3). Accordingly, the control circuit cannot determine the actual X/Y rectangular coordinates of points M2 and M4 based on which light-receiving elements fail to receive a light beam during a scan cycle due to blockage of the light beams, such as the light beams 140, 142, 144, 146. These points, except points M2 and M4, are not actual points and thus are defined as phantom points.
However, there are many applications requiring “multi-point” touch in order to provide users with a more friendly user interface and better interaction between people and machine, for example, Apple® iPod® Touch which provides a friendly multi-point touch interface or called a multi-touch interface. Still, in the technical field of optical touch panels, the feature of the “multi-point” touch has not been integrated thereto.